Large Scale Molecular Dynamics Simulations of Slip and Twinning in c-axis Compression of Magnesium Single Crystals
Yizhe Tang (Johns Hopkins University), Jaafar El-Awady (Johns Hopkins University)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium B
Wed 1:30 - 2:50
CIT 227
Twinning is one of the most prevalent deformation mechanism in HCP crystals. Recent experimental studies have suggested that twin nucleation during c-axis compression of Mg single crystals is size dependent. However, these studies have neglected the influence of the initial dislocation density in these crystals. To address this, in this study we perform large scale molecular dynamics simulations c-axis compression of Mg single crystals having different densities of pre-existing dislocation network and crystal sizes varying between 20 and 100 nm in diameter. From these simulations two twin nucleation mechanisms are identified, namely, surface-induced twin nucleation, and dislocation-induced twin nucleation. The former dominates at low dislocation densities, while the latter dominates when there are sufficient dislocations in the sample such that appropriate dislocation junctions and dislocation reactions can lead to twin nucleation. At intermediate dislocation densities neither of these two twin nucleation mechanisms are likely to exist, and plastic deformation is solely accommodated by c+a dislocation slip.